Temperate phage was induced from Streptococcus cremoris C3 and morphologically characterized by high-resolution electron micrographic techniques. Interspecies genetic transfer of lactose-fermenting ability by the temperate phage was demonstrated, using two lactose-negative (Lac) S. lactis strains as recipients. Plasmid transfer was confirmed by agarose gel electrophoresis. Transductant plasmid profiles were of three types-those containing no visible plasmid deoxyribonucleic acid, those possessing a 23-megadalton (Mdal) plasmid, and those containing a 23-Mdal plasmid and a 30-Mdal plasmid. A Lac transductant could serve as a donor of the lac determinants during solid-surface matings. These results add to previously published reports of inter- and intraspecies genetic transfer in dairy starter cultures.